Nano-sized, conductor or non-conductor particles are generally produced in a single gas phase or liquid phase (see Non-Patent Document 1).
Gas-phase methods are continuous processes suitable for high-speed mass production of highly pure particles and have reached a higher degree of technical maturity than other methods. Nevertheless, gas-phase methods still face the greatest challenge of improving the quality of nanoparticles themselves, with productivity (yield) and cost effectiveness (cost reduction and equipment/process simplification) also remaining to be improved. Liquid-phase methods, on the other hand, can produce less aggregated particles with a uniform particle diameter, but are similarly facing the challenge of improving cost effectiveness and functions (e.g., catalyst characteristics), as well as the quality of nanoparticles themselves.
Solid-phase methods are under development since there remains considerable room for improvement in nanoparticle quality, productivity and cost effectiveness.
On the other hand, technologies are known that supply plasma in a fluid (see Patent Document 1). Patent Document 1 reports a plasma generation method which includes the steps of: providing a fluid in a bath having therein separately-arranged electrodes constituting a cathode electrode and an anode electrode; forming a stream of air bubbles in the fluid in the vicinity of the cathode electrode; and applying a voltage between the cathode and anode electrodes to cause glow discharge in the air bubbles for plasma generation. Patent Document 1 also reports that submerged plasma generation leads to production of fine particles from metal ions etc., contained in the fluid.
Other reported technologies are directed to metal coating by utilizing plasma generated in a fluid (see Patent Documents 2-4).
Patent Document 1: Japanese Patent Application Laid-Open No. 2005-529455
Patent Document 2: Japanese Patent Application Laid-Open No. 2006-097082
Patent Document 3: Japanese Patent Application Laid-Open No. 2004-277812
Patent Document 4: Japanese Patent Application Laid-Open No. 2005-521794
Non-Patent Document 1: Chart for Supporting Patent Licensing (Patent Map) 2005, Ippan 18, Nanoparticle Production Technology (issued on March 2006, National Center for Industry Property Information and Training)